SEOUL, Feb. 27 (Yonhap) -- A local scholar claimed Wednesday an official hat that belonged to King Sejong (1418-1450), inventor of Korea's writing system hangeul, has been found in South Korea more than 500 years after it was stolen by Japanese invaders.

The discovery of the hat called "Ikseongwan," if confirmed, is expected to provide a new milestone in the study of Korean history as a rare relic from the early years of the Joseon Dynasty (1392-1910).

As important as the hat itself are a few pages of old documents related to the writing system called Hunminjeomgeum, literally meaning "proper sounds to instruct the people," which were found hidden inside the hat, according to the scholar.

"This is the Ikseongwan hat that King Sejong used and has a pattern of a dragon with four claws," Lee Sang-gyu, professor of Korean language and literature at Kyungpook National University, told reporters, adding that the hat is one of the royal relics looted by Japanese invaders during the two Japanese invasions of Korea in the 16th century.

The hat's presence was known last year when a local collector purchased it in Japan and brought it home, according to Lee's research team.

The team said the hat's embroidery of the four-clawed dragon pattern and inclusion of Hunminjeongeum-related old documents was the grounds for their presumption that the hat belonged to King Sejong.

Sejong changed the embroidery pattern on Joseon kings' gowns and hats into a five-clawed dragon in his later years on the throne, the team said, citing history records from the Joseon period.

The team said they have yet to disassemble the hat for fear of possible damage but believes the documents that can be seen through the hat's red-colored lining are the first part of a printed book of Hunminjeomeum Haerye that gives the detailed explanations and examples of each letter of the Korean alphabet.

As the collector has expressed his intent to donate the relics to the state, the team said they will soon analyze the documents inside the hat and make public the outcome through consultation with the nation's cultural heritage authority.